Semax, Selank and DSIP: The Research Landscape
A family built on the same design logic — a short fragment of a larger peptide, stabilised with a Pro-Gly-Pro extension — and a literature with its own characteristics.
A cluster of short peptides — Semax, Selank, DSIP, and a few others — occupies an unusual position in the research literature. Most were developed in Soviet and Russian institutes from the 1980s onward, and the resulting body of work is substantial but published largely in a separate literature from the Western mainstream.
The shared design logic
Almost all of them follow the same approach: take a short fragment of a larger endogenous peptide, then modify the ends to make it survive.
- Semax — the ACTH(4–7) fragment Met-Glu-His-Phe extended with Pro-Gly-Pro at the C-terminus. The tripeptide extension is the stabilising element; the ACTH fragment carries the activity without the hormonal effects of the parent.
- Selank — the tetrapeptide tuftsin (Thr-Lys-Pro-Arg) with the same Pro-Gly-Pro extension.
- DSIP — a nine-residue peptide isolated in the 1970s from the cerebral venous blood of rabbits in induced sleep, and named for the observation rather than a mechanism.
The recurring Pro-Gly-Pro motif is worth noticing. Proline’s ring constrains the backbone and is poorly accepted by many proteases, so the extension both stabilises the peptide and slows enzymatic attack. It is a deliberate design element that shows up across the whole family.
Why the literature looks the way it does
Several characteristics recur, and being clear-eyed about them matters more than for most compound classes:
- A large share of primary work is in Russian-language journals, some of it not indexed in Western databases and much of it not translated. The volume of research is real; its accessibility is limited.
- Study sizes are often small and methodology varies.
- Mechanistic accounts are frequently incomplete. BDNF modulation is the most commonly proposed mechanism for Semax; for Selank, effects on GABAergic signalling and on enkephalin degradation are described. These are hypotheses supported by data, not settled pathways.
- Independent replication outside the originating institutes is limited for most of the class.
None of that makes the compounds uninteresting. It does mean that “well-researched” and “well-replicated” are different claims, and only the first is straightforwardly true here.
Why they are analytically straightforward
The practical compensation is that these are easy molecules to verify. At four to nine residues:
- Coupling efficiency compounds over very few steps, so crude purity is high before purification
- Deletion sequences are few and well separated on a chromatogram
- Mass differences from a missing residue are large relative to the total mass and unmissable
- None of them carry disulfides, so there is no scrambling to worry about
A certificate for a short peptide should be clean and unambiguous: one dominant peak, an observed mass within a fraction of a dalton of theory. There is nowhere for an impurity to hide in a heptapeptide, which means anything less than tidy is a real signal rather than an artefact of difficulty.
Handling
Short, proline-rich, cysteine-free peptides are at the robust end. Standard practice covers them: sealed lyophilised storage, equilibration before opening, gentle reconstitution, refrigeration afterwards. Semax contains methionine and is therefore subject to oxidation — the +16 Da mass shift — so minimising headspace and light exposure is worthwhile.
Our Semax and Selank comparison covers the two compounds in detail, and the DSIP article covers the third.
All compounds are supplied strictly for laboratory research. We do not provide dosing information and nothing here describes use in humans.
All products and information referenced are for in-vitro research and laboratory use only. Nothing here is medical advice, and no therapeutic claim is made or implied.